People express more bias in their predictions than in their likelihood judgments.

What is it about?

Perhaps it goes without saying, but probabilities should inform predictions. When predicting whether a blue or green marble will be randomly drawn from a jar, a person should predict the more probable/frequent color. However, there may be times when predictions are substantially influenced by extra-evidentiary factors, such as desiring one outcome over another. We will report studies comparing the biasing influence of outcome desirability on people’s predictions versus likelihood judgments. Unlike prior studies that explored this issue by having people make forecasts for purely aleatory events for which probability-relevant information was provided in a numeric summary, we asked people for forecasts about sports events. The desirability of outcomes was manipulated, and people were asked to provide forecasts in the form of either predictions or likelihood judgments. Under specific circumstances, predictions reflected more bias than did likelihood judgments. This occurred even when scale differences for predictions and likelihood judgments were minimized. We suggest that people interpret solicitations of predictions vs. likelihood judgments to carry slightly different emphases on choosing one’s stance regarding the outcomes vs. assessing the balance of evidence relevant to those outcomes.

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Photo by milos tomasevic on Unsplash

Photo by milos tomasevic on Unsplash